This variable was introduced in 6.0.2 to solve a problem with the indexer.
SPR# PMGL5E3VT4 - Fixed memory problems when using a single HTTP search query. Disable the "not" keyword from the search query when "not" is the first token in the string and un-quoted "test" follows the "not" token. This effectively changes the first "not" from the "not" keyword or just "not" text. Use FTG_DISABLE_NOT=1 to enact this functionality. Example: if the query equals: not enough quota then translate to "not enough quota". To activate, use notes.ini entry FTG_DISABLE_NOT=1